I am terrible on TV. I slouch, sneer, stammer, fidget, forget my lines and swallow the ends of my words. It rankles, because I know inside I am scintillating, sensitive and sincere. Television can make any fool look like an intellectual. Newsreaders can contrive to look nice and even the worst presenters can seem sensible, but I come over as a shifty subversive. The single television programme I have presented was so awful that even my mother couldn’t find a good word for it. After a catastrophic radio show last year, when I addressed the interviewer by the wrong name throughout, I swore I’d never do broadcasting again.

Until now, that is. I have my first novel out next month, which is called Do It Again, and the PR people inform me you just have to get out there and promote it. Scotland one day, the south coast of England the next. It’s going to be hectic and I have to get my act together. Which is how I find myself being scrutinised for televisual potential by two svelte creatures from Public Image Ltd, while cameraman Alastair focuses on my trembling upper lip. Public Image is the outfit which has been teaching MPs how to look good on TV. They also groom executives from major companies in everything from corporate presentations to handling broadcast interrogation, but as far as I’m concerned, if they can make politicians look like real people, they are good enough for me.

‘He blinks a lot, doesn’t he?’ says Diana, the speech specialist, studying my image on a video monitor. ‘And the crossed legs look defensive. But the voice isn’t bad.’ Jeannie, who is introduced to me as Public Image’s ‘charisma consultant’, takes a step backwards to study the general posture. ‘Needs to get his bottom back in the sofa. And the jacket makes him look a bit deformed. Where does he get his clothes from?’

‘Honesty is the most important thing,’ says Diana. ‘We don’t want to turn people into actors. We want to bring out the personality. And of course speech is most important too. Lots of politicians don’t breathe properly, so they have to shout. They give themselves sore throats and polyps on the vocal chords. Breathe from the diaphragm and you can speak quite loudly and for quite a long time without strain. Then most importantly, there are the three E’s: Energy, Enthusiasm and Enjoyment. And do try to stop blinking.’

And so, as I breathe from the diaphragm, clench my eyelids apart and desperately try to project honesty as well as the three Es at once, the camera rolls. ‘Today we are visiting the home of Martyn Harris,’ says Diana dishonestly, ‘a journalist who has recently published his first novel Do It Again. So, what can you tell us about the plot, Martyn?’ ‘Umm …’ A long pause. ‘Errr … ‘ A longer pause. ‘Tee hee, hargh … ’ An asinine giggle. ‘All right Alastair,’ says Diana patiently, ‘we’ll try that again.’

We try it again, many, many times, each time chipping away at another tic and mannerism and gaucherie. On the second run-through, my crossed legs keep bobbing up and down, which makes me look as if I want to run away (I do, I do). On the third run they are uncrossed, but my hands are clenched in my lap. On the fourth I have wrenched my hands from my lap, but now they are fiddling with my ears. On the fifth, I’m throwing away the ends of my sentences, which sounds as if I think my audience is thick (I don’t really).

Television does curious things to your face, dragging it towards the edges of the screen. If you have a long face, as I have, it makes you look like a cadaverous mule. It emphasises the darkness of lipstick and eyeshadow, so make-up should be minimal, and used mainly to soften facial shadows. Does Diana think it is wicked, I wonder, to mould politicians in this way? ‘As soon as anyone gets on telly these days, we expect them to be as good as the professionals, because that’s where we get our standards from. It’s unfair, but that’s the way of the world. As for the ethics, I leave that to others and get on with my job.’

And it’s a job she does very well, because on the final run-through, after three hours or so, I really don’t look too bad. Steady gaze, breathing from the diaphragm, no twitches, no blinking. Not a consummate professional in the business, but not bad.

I’m brimming with honesty, energy, enthusiasm and enjoyment and I’m talking a lot of twaddle, but you’d hardly notice. When you watch politicians on TV, you’ll see a lot more just like me.